Shock or vibration attenuating mounts and other devices employing rubber or a similar elastomeric material for load supporting and motion accommodating purposes are well known to those skilled in the art. Such material has excellent spring-like properties, but the use thereof is subject to certain practical limitations. When the loads imposed upon the elastomer are of very great magnitude, the amount of elastomeric material that must be employed may be so great as to cause the mount or other device to be of an excessive size in relation to the size of the site of its intended utilization. Additionally, elastomeric devices are unsuitable for use in locations where exposure to corrosive chemicals, extreme temperatures or other adverse environmental conditions will significantly impair the properties and/or useful life of the elastomer.
As an alternative to the use of elastomeric materials, it has heretofore been proposed to employ metallic materials for the dual purposes of load support and motion accommodation in utilizations where space is limited and/or adverse environmental conditions are present. Since solid metallic bodies are too stiff to accommodate large amplitude motions, the materials previously proposed for such use have usually been in the form of compacted masses of discreet metallic strands or the like. In addition to good resistance to adverse environmental conditions, the properties desired for such materials are similar to those possessed by elastomer. That is, the material should: (1) undergo significant elastic strain over an appreciable range of significant applied stresses; (2) while its modulus remains substantially constant; (3) irrespective of the particular direction of load application. Further, the material should be highly durable and not subject to premature failure under repeated cyclic loading over a long period of time. Insofar as applicants are aware, none of the metallic wire materials heretofore proposed possess all of the aforesaid desired properties and characteristics.
More specifically in the foregoing regard, the compressed metallic material now commonly used is comprised of high strength metallic wires which are first knitted together to form a mesh-like knitted fabric wherein adjacent sections of the wires are innerconnected by generally coplanar loops formed along their lengths during and by the knitting process. As in any knitted fabric, the capability of the innerconnected loops for movement relative to each other differs dramatically in different directions: i.e., the fabric is highly anisotropic. Following formation of the knitted fabric, layers of it are arranged in superimposed relationship to one another. The superimposed layers may and usually are then subjected to a gear-tooth or similar crimping or corrugating process, and are in any event then compressed within a die or the like to impart a desired shaped and density to the finished material. Notwithstanding the number and considerable expense of the manufacturing steps used in its formation, the aforesaid material has stress/strain characteristics which are significantly nonlinear in any direction and which are exceedingly anisotropic. A plot of such characteristics along two mutually perpendicular axes of the material produces curves which are each very nonlinear, eventually cross each other, have significantly different slopes at any given strain level, and which reflect that the compression stiffness of the material in one axial direction is only approximately one-half of its compression stiffness in the other axial direction. Additionally, it has been found that the aforesaid material formed of knitted metal wires tends to disintegrate when subjected to cyclic loading of substantial magnitude and duration. It is believed that this lack of durability is attributable in large part to the individual wires of the finished material having a multiplicity of localized stress concentrations or "risers" spaced along the lengths thereof. Although the wires selected for use in the material are usually smooth-surfaced ones formed of drawn stainless steel or the like, the process of knitting such wires together inherently produces a multiplicity of stress risers within the wires at spaced locations along their lengths. The step of crimping superimposed layers of the knitted fabric then adds additional stress risers and/or aggrevates those previously generated by the knitting process. The final step of compressing the superimposed layers of knitted fabric produces still other stress risers and further aggrevates those already present within the wires. The generation of some stress risers during the compression step is necessary to impart a desired final shape and density to the material. However, the stress risers generated by the knitting and, if employed, crimping processes are unnecessary and undesirable ones. Additionally, it is believed that compression of a knitted wire fabric may produce more stress risers than are required for shaping and/or densification purposes, due to the inability of the innerconnected and essentially two-dimensional loops of the knitted wires to significantly re-orient themselves in planes which are substantially perpendicular to the distorting forces imposed thereon. In any event, the prior-art metallic materials formed of superimposed and compressed layers of knitted metal fabric or mesh tend to disintegrate into small metallic particles when subjected to cyclic loads of significant magnitude and duration. Such disintegration not only causes the material to lose such spring-like motion accommodating properties as it originally possessed, but additionally results in the discharge from the material of small wire fragments which may seriously damage adjacent machinery components or the like.